The present invention relates to a light emitting device, preferably a light emitting diode device, providing a light beam with limited dispersion. The device is particularly, but not exclusively, intended for use in a so called red dot sight mounted on a weapon. The red dot is projected on a lens as an aiming point, the gunner looking through the lens when aiming.
In present red dot sights it is customary to use a battery powered light emitting diode (LED) as the light source. The LED shall provide a narrow and distinct beam of light, whichxe2x80x94as appears from the name of the devicexe2x80x94may be red. The shape of the beam may vary but is most often circular, so that a red dot appears for the gunner in the sight. With the use of a conventional LED the beam is created by placing a mask with a narrow hole at the end of the plastic bulb of the LED. The normally desired circular beam is created by a circular hole.
Due to the presence of the bulb the mask will be at a certain distance from the light emitting surface of the LED, for example 2 mm or more. As the light dispersion increases with the square of the distance, the efficiency of the device is not satisfactory, which in turn means that the battery power will be consumed comparatively quickly.
Another problem in the conventional sight is that the intensity of the projected light varies when looking at different areas of the surface of the lens.
The main object of the invention is to remove the above stated drawbacks and to attain a light emitting device which is more efficient in providing a light beam with limited dispersion and which allows that the light emitting surface of the LED always covers the whole pattern of the mask.
According to the invention this is accomplished in that a light-impermeable mask with a hole for light is arranged on or in direct vicinity to a light emitting surface of a light emitting element in the device.
In a red dot sight use is made of a reflecting and focusing lens. With the above arrangement the light emitting surface is directly visible from every point of the lens.
With the same light intensity as provided by a conventional device the diode current may be decreased by a factor of 5-10, resulting in a corresponding increase of the battery life.